Method of making diffraction grating device, diffraction grating device, and apparatus for making the same

ABSTRACT

The present invention relates to a method of making a diffraction grating device, in which an optical waveguide is irradiated, by way of a phase grating, with light capable of inducing a refractive index modulation in an optical waveguide region of the optical waveguide so as to form a diffraction grating in the optical waveguide region. In the present invention, when modulating the refractive index of the optical waveguide region of an optical fiber, the intensity of refractive index modulation inducing light emitted from a laser light source so as to irradiate the phase grating is adjusted according to individual positions on the phase grating. Alternatively, the scanning speed of a mirror scanned by a stage is adjusted according to the individual positions on the phase grating. Here, the amount of irradiation of refractive index modulation inducing light at each position on the phase grating is adjusted so as to cancel the diffraction efficiency distribution of phase grating. The present invention can make a diffraction grating device having a desirable characteristic even when the diffraction efficiency distribution of phase grating deviates from its desirable distribution.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a method of making a diffractiongrating device in which an optical waveguide is irradiated, by way of aphase grating, with light capable of inducing a refractive indexmodulation in an optical waveguide region of the optical waveguide so asto form a diffraction grating in the optical waveguide region; thediffraction grating device made by this method; and an apparatus formaking the same.

[0003] 2. Related Background Art

[0004] Diffraction grating device has diffraction grating formed inoptical waveguide region of optical waveguide (encompassing both opticalfiber and planar optical waveguide) and is used as optical filter andthe like. Such a diffraction grating device is manufactured as follows.Namely, by way of a phase grating, an optical waveguide is irradiatedwith a predetermined wavelength of light capable of inducing arefractive index modulation (which is ultraviolet light in general, andwill hereinafter be referred to as “refractive indexmodulation inducinglight”). Then, interference fringes of the refractive index modulationinducing light are generated in an optical waveguide region of theoptical waveguide. Hence, the refractive index at a predetermined partof the optical waveguide region provided with the interference fringesis modulated, whereby a diffraction grating is formed.

[0005] Here, laser light emitted from a light source such as a KrF laserlight source, which outputs the refractive index modulation inducinglight, has a luminous flux diameter smaller than the length of thediffraction grating to be manufactured. As a consequence, a diffractiongrating having a desirable length is made when the refractive indexmodulation inducing light is made incident on the phase grating whilebeing scanned in a longitudinal direction of the optical waveguide.

SUMMARY OF THE INVENTION

[0006] The inventors have studied the conventional technique mentionedabove and, as a result, have found a problem as follows. Namely, whenmaking a diffraction grating, e.g., when making a uniform diffractiongrating, a phase grating having a uniform diffraction efficiencydistribution within a plane should be used. However, since thediffraction efficiency distribution of phase grating is not always setuniformly within a plane, a nonuniform diffraction grating may be madeeven if a uniform diffraction grating is intended to be made. Thus, theabove-mentioned conventional technique has been problematic in thatdiffraction grating having desirable characteristics cannot be made ifthe diffraction efficiency distribution of a phase grating deviates fromits desirable distribution.

[0007] For overcoming the above-mentioned problem, it is an object ofthe present invention to provide a method of making a diffractiongrating device which can make a diffraction grating having a desirablecharacteristic even when the diffraction efficiency distribution ofphase grating deviates from a desirable distribution, the diffractiongrating device made by this method, and an apparatus for making thesame.

[0008] The present invention provides a method of making a diffractiongrating device, in which an optical waveguide is irradiated, by way of aphase grating, with refractive index modulation inducing light capableof inducing a refractive index modulation in an optical waveguide regionof the optical waveguide so as to form a diffraction grating in theoptical waveguide region; the method comprising: (1) a diffractionefficiency distribution measuring step of measuring a diffractionefficiency distribution of the phase grating; and (2) a refractive indexmodulating step of irradiating the optical waveguide with the refractiveindex modulation inducing light by way of the phase grating with anamount of irradiation of the refractive index modulation inducing lightat each position on the phase grating being adjusted according to thediffraction efficiency distribution measured in the diffractionefficiency distribution measuring step, so as to modulate a refractiveindex of the optical waveguide region.

[0009] Preferably, in the method of making a diffraction grating devicein accordance with the present invention, the diffraction efficiencydistribution measuring step is carried out prior to the refractive indexmodulating step. Alternatively, it is preferred that the diffractionefficiency distribution measuring step be carried out simultaneouslywith the refractive index modulating step, and that the amount ofirradiation of refractive index modulation inducing light at eachposition on the phase grating be feedback-controlled according to thediffraction efficiency distribution of phase grating measured in thediffraction efficiency distribution measuring step.

[0010] In the method of making a diffraction grating device inaccordance with the present invention, it is preferred that therefractive index modulation inducing light be made incident on the phasegrating while being scanned in a longitudinal direction of the opticalwaveguide in the refractive index modulating step, and that theintensity of the refractive index modulation inducing light irradiatingeach position on the phase grating be adjusted upon the scanning.

[0011] In the method of making a diffraction grating device inaccordance with the present invention, it is preferred that therefractive index modulation inducing light be made incident on the phasegrating while being scanned in a longitudinal direction of the opticalwaveguide in the refractive index modulating step, and that the scanningspeed of the refractive index modulation inducing light irradiating eachposition on the phase grating be adjusted upon the scanning.

[0012] The present invention provides a diffraction grating device madeby the above-mentioned method of making a diffraction grating device.

[0013] The present invention provides an apparatus for making adiffraction grating device, in which an optical waveguide is irradiated,by way of a phase grating, with refractive index modulation inducinglight capable of inducing a refractive index modulation in an opticalwaveguide region of the optical waveguide so as to form a diffractiongrating in the optical waveguide region; the apparatus comprising: (1)diffraction efficiency distribution measuring means for measuring adiffraction efficiency distribution of the phase grating; and (2)refractive index modulating means for irradiating the optical waveguidewith the refractive index modulation inducing light by way of the phasegrating with an amount of irradiation of the refractive index modulationinducing light at each position on the phase grating being adjustedaccording to the diffraction efficiency distribution measured by thediffraction efficiency distribution measuring means, so as to modulate arefractive index of the optical waveguide region.

[0014] Preferably, in the apparatus for making a diffraction gratingdevice in accordance with the present invention, the diffractionefficiency distribution measuring means measures the diffractionefficiency distribution of the phase grating before the refractive indexmodulating means irradiates the phase grating with the refractive indexmodulation inducing light. Alternatively, it is preferred that thediffraction efficiency distribution measuring means measure thediffraction efficiency distribution of phase grating at the same timewhen the refractive index modulating means irradiates the phase gratingwith the refractive index modulation inducing light, and that therefractive index modulating means feedback-control the amount ofirradiation of refractive index modulation inducing light at eachposition on the phase grating according to the diffraction efficiencydistribution of phase grating measured by the diffraction efficiencydistribution measuring means.

[0015] In the apparatus for making a diffraction grating device, therefractive index modulating means may comprise irradiating means formaking the refractive index modulation inducing light incident on thephase grating while scanning the refractive index modulation inducinglight in a longitudinal direction of the optical waveguide, andirradiation intensity adjusting means for adjusting the intensity of therefractive index modulation inducing light irradiating each position onthe phase grating when the refractive index modulation inducing light isscanned by the irradiating means.

[0016] In the apparatus for making a diffraction grating device, therefractive index modulating means may comprise irradiating means formaking the refractive index modulation inducing light incident on thephase grating while scanning the refractive index modulation inducinglight in a longitudinal direction of the optical waveguide, and scanningspeed adjusting means for adjusting the scanning speed of the refractiveindex modulation inducing light irradiating each position on the phasegrating when the refractive index modulation inducing light is scannedby the irradiating means.

[0017] The present invention provides an apparatus for making adiffraction grating device, in which a diffraction grating is made in anoptical waveguide region of an optical waveguide, the apparatuscomprising: (1) a light source for emitting refractive index modulationinducing light capable of inducing a refractive index modulation in theoptical waveguide region; (2) a phase grating for diffracting therefractive index modulation inducing light emitted from the lightsource; (3) a mirror for reflecting the refractive index modulationinducing light emitted from the light source so as to make therefractive index modulation inducing light incident on the phasegrating; (4) a moving unit for moving the mirror along a longitudinaldirection of the optical waveguide; and (5) an irradiation intensitycontrol unit for controlling the irradiation intensity of the refractiveindex modulation inducing light emitted from the light source.

[0018] The present invention provides an apparatus for making adiffraction grating device, in which a diffraction grating is made in anoptical waveguide region of an optical waveguide, the apparatuscomprising: (1) a light source for emitting refractive index modulationinducing light capable of inducing a refractive index modulation in theoptical waveguide region; (2) a phase grating for diffracting therefractive index modulation inducing light emitted from the lightsource; (3) a mirror for reflecting the refractive index modulationinducing light emitted from the light source so as to make therefractive index modulation inducing light incident on the phasegrating; (4) a moving unit for moving the mirror along a longitudinaldirection of the optical waveguide; and (5) a speed control unit forcontrolling, according to a diffraction efficiency distribution of thephase grating, the moving speed of the mirror moved by the moving unit.

[0019] The apparatus for making a diffraction grating device inaccordance with the present invention may further comprise alight-receiving device provided so as to sandwich the phase gratingbetween the light-receiving device and the mirror.

[0020] The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus are not to beconsidered as limiting the present invention.

[0021] Further scope of applicability of the present invention willbecome apparent from the detailed description given hereinafter.However, it should be understood that the detailed description andspecific examples, while indicating preferred embodiments of theinvention, are given by way of illustration only, since various changesand modifications within the spirit and scope of the invention willbecome apparent to those skilled in the art from this detaileddescription.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022]FIG. 1 is a diagram schematically showing the apparatus for makinga diffraction grating device in accordance with a first embodiment;

[0023]FIG. 2 is a view showing how the diffraction efficiencydistribution of a phase grating is measured by the apparatus for makinga diffraction grating device in accordance with the first embodiment;

[0024]FIG. 3A is a graph showing the diffraction efficiency distributionof a phase grating for a first case;

[0025]FIG. 3B is a graph showing a distribution of amount of irradiationof refractive index modulation inducing light with respect to the phasegrating for the first case;

[0026]FIG. 3C is a graph showing the degree of refractive indexmodulation in an optical waveguide region of an optical fiber for thefirst case;

[0027]FIG. 4A is a graph showing the diffraction efficiency distributionof a phase grating for a second case;

[0028]FIG. 4B is a graph showing a distribution of amount of irradiationof refractive index modulation inducing light with respect to the phasegrating for the second case;

[0029]FIG. 4C is a graph showing the degree of refractive indexmodulation in an optical waveguide region of an optical fiber for thesecond case;

[0030]FIG. 5A is a graph showing the diffraction efficiency distributionof the phase grating for a third case;

[0031]FIG. 5B is a graph showing a distribution of amount of irradiationof refractive index modulation inducing light with respect to the phasegrating for the second case;

[0032]FIG. 5C is a graph showing the degree of refractive indexmodulation in an optical waveguide region of an optical fiber for thethird case;

[0033]FIG. 6 is a diagram schematically showing a diffraction efficiencydistribution measuring unit for measuring the diffraction efficiencydistribution of a phase grating; and

[0034]FIG. 7 is a diagram schematically showing the apparatus for makinga diffraction grating device in accordance with a second embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] In the following, embodiments of the present invention will beexplained in detail with reference to the accompanying drawings. In theexplanation of drawings, constituents identical to each other will bereferred to with numerals or letters identical to each other, withoutrepeating their overlapping descriptions. Though the followingexplanation mainly relates to cases where an optical fiber is employedas an optical waveguide, it is similarly applicable to planar opticalwaveguides formed on planar substrates.

[0036] To begin with, a first embodiment of the method of making adiffraction grating device in accordance with the present invention,diffraction grating device made by this method, and apparatus for makingthe same will be explained.

[0037]FIG. 1 is a diagram schematically showing an apparatus 10 formaking a diffraction grating device in accordance with the firstembodiment. This apparatus 10 comprises a laser light source 11, a slit12, a mirror 13, a stage 14 equipped with a motor 14 a, a phase grating15, and a control unit 16 for controlling the apparatus 10. Thisapparatus 10 is configured such that an optical fiber (opticalwaveguide) 90 to be formed with a diffraction grating is disposeddirectly under the phase grating 15.

[0038] The optical fiber 90 has a core region 91 located at the centerthereof, and a cladding region 92 surrounding the core region 91. Thoughthe light guided through the optical fiber 90 propagates while beingconfined in the core region 91, a part of the energy of light alsoexists in the cladding region 92 in the vicinity of the core region 91.Namely, the optical waveguide region of the optical fiber 90 isconstituted by the core region 91 and the part of cladding region 92 inthe vicinity of the core region 91. While the optical fiber 90 is mainlycomposed of silica glass, the optical waveguide region (at least thecore region 91) is doped with GeO₂. As a consequence, if the opticalfiber 90 is irradiated with refractive index modulation inducing light,then the refractive index of the region doped with GeO₂ is modulatedaccording to the intensity of irradiation.

[0039] The laser light source 11 is a light source for outputting therefractive index modulation inducing light. As the light source, anexcimer laser light source (e.g., KrF laser light source or the like)capable of emitting ultraviolet laser light is suitably used.Preferably, the intensity of refractive index modulation inducing lightemitted from the laser light source 11 is variable.

[0040] Of the refractive index modulation inducing light outputted fromthe laser light source 11, the part entering an opening 12A of the slit12 passes therethrough so as to be made incident on the mirror 13. Themirror 13 reflects the refractive index modulation inducing light passedthrough the opening 12A of slit 12, so as to make it incident on thephase grating 15. The mirror 13 can be moved in the longitudinaldirection of the optical fiber 90 by the stage 14 having the motor 14 a.When the mirror 13 is moved as such, the refractive index modulationinducing light can be made incident on the phase grating 15 while beingscanned in the longitudinal direction of the optical fiber 90.

[0041] The phase grating 15 is formed with projections and depressionshaving a predetermined period on the side (where the optical fiber 90 isplaced) opposite from the side on which the refractive index modulationinducing light reflected by the mirror 13 is incident, and diffracts theincident refractive index modulation inducing light. Also, the phasegrating 15 forms interference fringes of outputted (+)first-orderdiffracted light and (−)first-order diffracted light, whereby arefractive index modulating area corresponding to these interferencefringes is formed in the optical waveguide region of optical fiber 90.The optical fiber 90 in which the refractive index modulating area isformed in the optical waveguide region acts a diffraction gratingdevice.

[0042] The control unit 16 is constituted by a microcomputer, a memory,and the like. The control unit 16 is electrically connected to the lightsource 11, so as to control the intensity of refractive index modulationinducing light emitted from the light source 11. Also, the control unit16 is electrically connected to the motor 14 a of stage 14, so as tocontrol the moving speed of mirror 13.

[0043] In the method of making a diffraction grating device inaccordance with this embodiment, the diffraction efficiency distributionof phase grating 15 is initially measured, and then a refractive indexmodulating area 94 is formed in the optical waveguide region of opticalfiber 90 with the amount of irradiation of refractive index modulationinducing light at each position of the phase grating 15 being adjustedaccording to the measured diffraction efficiency distribution of phasegrating 15. When measuring the diffraction efficiency distribution ofphase grating 15, as shown in FIG. 2, the respective intensities ofzero-order light, (+)first-order light, and (−)first-order lightoutputted from the phase grating 15 are measured by means oflight-receiving devices 6 to 8 or the like in the apparatus 10 formaking the diffraction grating device shown in FIG. 1 while the mirror13 is moved in the longitudinal direction of optical fiber 90 by thestage 14 in the state without the optical fiber 90. Then, thediffraction efficiency distribution of phase grating 15 is determinedaccording to the individual intensities. In this embodiment, theapparatus 10 for making a diffraction grating device may comprise thelight-receiving devices 6 to 8.

[0044] When making the diffraction grating 94 in the optical waveguideregion of optical fiber 90, the intensity of refractive index modulationinducing light emitted from the laser light source 11 so as to be madeincident on the phase grating 15 is adjusted by the control unit 16according to individual positions on the phase grating 15.Alternatively, the motor 14 a of stage 14 is controlled by the controlunit 16, so as to regulate the moving speed of mirror 13, such that thescanning speed of mirror 13 is adjusted according to the individualpositions on the phase grating 15. Thus, the amount of irradiation ofthe refractive index modulation inducing light at each position of thephase grating 15 is adjusted. Here, the amount of irradiation of therefractive index modulation inducing light with respect to the phasegrating 15 is adjusted so as to cancel the diffraction efficiencydistribution of phase grating 15.

[0045]FIGS. 3A, 4A, and 5A are graphs showing respective diffractionefficiency distributions of the phase grating 15 for first to thirdcases. FIGS. 3B, 4B, and 5B are graphs showing respective distributionsof amount of irradiation of refractive index modulation inducing lightwith respect to the phase grating 15 for these cases. FIGS. 3C, 4C, and5C are graphs showing respective degrees of refractive index modulationin the optical waveguide region of optical fiber 90 for these cases.

[0046] In the first case, as shown in FIG. 3A, the diffractionefficiency of phase grating 15 is the highest in the vicinity of thecenter of the phase grating 15 in the longitudinal direction thereof anddecreases toward its marginal areas. Here, the amount of irradiation ofrefractive index modulation inducing light with respect to the phasegrating 15 is adjusted so as to become uniform in the longitudinaldirection as shown in FIG. 3B. Then, the degree of refractive indexmodulation in the optical waveguide region of optical fiber 90 is thehighest in the vicinity of the center of the phase grating 15 in thelongitudinal direction thereof and decreases toward its marginal areasas shown in FIG. 3C, thus becoming nonuniform.

[0047] As shown in FIG. 4A, the diffraction efficiency of phase grating15 is the highest in the vicinity of the center of the phase grating 15in the longitudinal direction thereof and decreases toward its marginalareas in the second case as well. However, unlike the first case, theamount of irradiation of refractive index modulation inducing light withrespect to the phase grating 15 in the second case is adjusted so as tocancel the diffraction efficiency distribution of phase grating 15,i.e., so as to become the lowest in the vicinity of the center in thelongitudinal direction thereof and increase toward its marginal areas asshown in FIG. 4B. As a consequence, the degree of refractive indexmodulation in the optical waveguide region of optical fiber 90 becomeslongitudinally uniform as shown in FIG. 4C.

[0048] In the third case, the diffraction efficiency of phase grating 15is the lowest in the vicinity of the center in the longitudinaldirection thereof and increases toward its marginal areas as shown inFIG. 5A. The amount of irradiation of refractive index modulationinducing light with respect to the phase grating 15 in the third case isadjusted so as to cancel the diffraction efficiency distribution ofphase grating 15, i.e., so as to become the highest in the vicinity ofthe center in the longitudinal direction thereof and decrease toward itsmarginal areas as shown in FIG. 5B. As a consequence, the degree ofrefractive index modulation in the optical waveguide region of opticalfiber 90 becomes longitudinally uniform as shown in FIG. 5c.

[0049] The diffraction efficiency distribution of phase grating 15 maybe measured by means of the apparatus 10 for making a diffractiongrating device shown in FIGS. 1 and 2, or a diffraction efficiencydistribution measuring unit separate therefrom. FIG. 6 is a schematicdiagram showing a diffraction efficiency distribution measuring unit 20for measuring the diffraction efficiency distribution of phase grating15.

[0050] The diffraction efficiency distribution measuring unit 20comprises a stage 21 mounting the phase grating 15 and having a motor 21a for moving the latter; a mirror 22 for causing the refractive indexmodulation inducing light outputted from the laser light source 11 to beincident on the phase grating 15; acondenser lens 23; andlight-receiving devices 24 to 26 for measuring the respectiveintensities of zero-order light, (+)first-order diffracted light, and(−)first-order diffracted light outputted from the phase grating 15.

[0051] In the diffraction efficiency distribution measuring apparatus20, the refractive index modulation inducing light outputted from thelaser light source 11 is reflected by the mirror 22 and then iscollected by the condenser lens 23, so as to irradiate the phase grating15 mounted on the stage 21. The intensity of the zero-order lightgenerated along with the irradiation of the phase grating 15 with therefractive index modulation inducing light is measured by thelight-receiving device 24, the intensity of thus generated(+)first-order diffracted light is measured by the light-receivingdevice 25, and the intensity of thus generated (−)first-order diffractedlight is measured by the light-receiving device 26. As the intensity ofeach diffracted light is measured while the phase grating 15 is moved bythe stage 21, the diffraction efficiency distribution of phase grating15 is determined.

[0052] The diffraction efficiency distribution measuring apparatus 20may use other laser light sources in place of the laser light source 11for outputting the refractive index modulation inducing light, and thediffraction efficiency distribution of phase grating 15 at thewavelength of refractive index modulation inducing light may bedetermined according to the diffraction efficiency distribution of phasegrating 15 measured by use of these other laser light sources.

[0053] In this embodiment, as in the foregoing, the diffractionefficiency distribution of phase grating 15 is initially measured, andthen diffraction grating 94 is formed in the optical waveguide region ofoptical fiber 90 with the amount of irradiation of refractive indexmodulation inducing light at each position of the phase grating 15 beingadjusted according to the measured diffraction efficiency distributionof phase grating 15. As a consequence, even when the diffractionefficiency of phase grating 15 is not uniform within a plane, adiffraction grating device having a desirable characteristic can bemade.

[0054] A second embodiment of the method of making a diffraction gratingdevice in accordance with the present invention, diffraction gratingdevice made by this method, and apparatus for making the same will nowbe explained.

[0055]FIG. 7 is a diagram schematically showing an apparatus 30 formaking a diffraction grating device in accordance with the secondembodiment. The apparatus 30 for making a diffractiong rating device inaccordance with this embodiment further comprises light-receivingdevices 31 to 33 in addition to the apparatus 10 for making adiffraction grating device in accordance with the first embodiment.

[0056] Each of the light-receiving devices 31 to 33 is provided so as tosandwich the phase grating 15 between the mirror 13 and the respectivelight-receiving device, so that the optical fiber 90 is set between thephase grating 15 and the light-receiving devices 31 to 33. Thelight-receiving device 31 measures the intensity of the zero-order lightgenerated along with the irradiation of phase grating 15 with therefractive index modulation inducing light. The light-receiving device32 measures the intensity of the (+)first-order diffracted lightgenerated along with the irradiation of phase grating 15 with therefractive index modulation inducing light. The light-receiving device33 measures the intensity of the (−)first-order diffracted lightgenerated along with the irradiation of phase grating 15 with therefractive index modulation inducing light. Thus, the diffractionefficiency distribution of phase grating 15 is determined according tothe intensities of light received by the light-receiving devices 31 to33.

[0057] In this embodiment, the diffraction efficiency distribution ofphase grating 15 is measured at the same time when the refractive indexof optical waveguide region in the optical fiber 90 is modulated, andthe amount of irradiation of refractive index modulation inducing lightat each position of the phase grating 15 is feedback-controlledaccording to thus measured diffraction efficiency distribution of phasegrating 15.

[0058] Namely, when measuring the diffraction efficiency distribution ofphase grating 15, the diffraction grating is formed in the opticalwaveguide region of optical fiber 90 while the mirror 13 is moved in thelongitudinal direction of optical fiber 90 by the stage 14 in the statewhere the optical fiber 90 is set between the phase grating 15 and thelight-receiving devices 31 to 33 in the apparatus 30 for making adiffraction grating device shown in FIG. 7. At the same time, therespective intensities of the zero-order light, (+)first-order light,and (−)first-order light outputted from the phase grating 15 arereceived by the light-receiving devices 31 to 33, and the diffractionefficiency distribution of phase grating 15 is determined according tothus received light intensities.

[0059] When forming the diffraction grating 94, the light source 11 iscontrolled by the control unit 16, such that the intensity of therefractive index modulation inducing light emitted from the laser lightsource 11 so as to be made incident on the phase grating 15 is adjustedaccording to the individual positions on the phase grating 15.Alternatively, the motor 14 a of stage 14 is controlled by the controlunit 16, so as to regulate the moving speed of mirror 13, such that thescanning speed of mirror 13 is adjusted according to the individualpositions on the phase grating 15. Here, the amount of irradiation ofrefractive index modulation inducing light at each position on the phasegrating 15 is feedback-controlled according to the measured diffractionefficiency distribution of phase grating 15 so as to cancel thediffraction efficiency distribution of phase grating 15.

[0060] In this embodiment, the relationship among the diffractionefficiency distribution of phase grating 15, the distribution of amountof irradiation of refractive index modulation inducing light withrespect to the phase grating 15, and the degree of refractive indexmodulation is similar to that explained with reference to FIGS. 3A to3C, 4A to 4C, and 5A to 5C in the first embodiment.

[0061] In this embodiment, as in the foregoing, the diffractionefficiency distribution of phase grating 15 is measured at the same timewhen the diffraction grating 94 is formed in the optical waveguideregion of optical fiber 90, and the amount of irradiation of refractiveindex modulation inducing light at each position of the phase grating 15is feedback-controlled according to thus measured diffraction efficiencydistribution of phase grating 15. As a consequence, even when thediffraction efficiency of the phase grating 15 is not uniform within aplane, a diffraction grating device having a desirable characteristiccan be made. In particular, a diffraction grating device having adesirable characteristic can be made in this embodiment even when theintensity of the refractive index modulation inducing light emitted fromthe laser light source 11 is unstable.

[0062] Here, when a plurality of signals at intervals of 0.4 nm(approximately equivalent to 50 GHz) are made incident on a fibergrating, there is a correlation between the value of reflection (sidelobe) of the spectrum at a wavelength separated by 2 channels (0.8 nm)or more from the center wavelength of the fiber grating and the amountof fluctuation in diffraction efficiency of a phase grating used formaking the fiber grating. Therefore, using a phase grating whose amountof fluctuation of zero-order diffraction efficiency is 0.35, theinventors studied the side lobe in each of a fiber grating made with thefluctuation of diffraction efficiency being corrected by the method ofmaking a diffraction grating device in accordance with this embodimentand a fiber grating made without correcting the fluctuation ofdiffraction efficiency. The result indicates that, while the side lobeof the fiber grating made without correcting the fluctuation ofdiffraction efficiency is as much as about −22 dB, the side lobe of thefiber grating made with the fluctuation of diffraction efficiency beingcorrected is −28 dB or less, thereby improving a characteristic. Thevalue of −28 dB or less is on a par with that of a side lobe obtainedwhen the amount of fluctuation of zero-order diffraction efficiency is0.01 or less.

[0063] Without being restricted to the above-mentioned embodiments, thepresent invention can be modified in various ways. For example, whilethe above-mentioned embodiments relate to the making of a diffractiongrating device in which the degree of refractive index modulation in theoptical waveguide region of optical fiber 90 is longitudinally uniform,the same also applies to the making of a diffraction grating device inwhich the degree of refractive index modulation has a predetermineddistribution which is not longitudinally uniform.

[0064] Though the above-mentioned embodiments relate to the case wherethe optical waveguide is an optical fiber, the same also applies toplanar optical waveguides formed on planar substrates.

[0065] Also, in addition to or in place of the respective intensities ofzero-order light, (+)first-order diffracted light, and (−)first-orderdiffracted light, the respective intensities of (+)second-orderdiffracted light and (−)second-order diffracted light may be measured,so as to control the amount of irradiation of refractive indexmodulation inducing light according to these intensities.

[0066] According to the present invention, as explained in detail in theforegoing, the diffraction efficiency distribution of a phase grating ismeasured by diffraction efficiency distribution measuring means in adiffraction efficiency distribution measuring step. Then, in arefractive index modulating step, the amount of irradiation ofrefractive index modulation inducing light at each position on the phasegrating is adjusted by refractive index modulating means according tothus measured diffraction efficiency distribution of phase grating,whereby a refractive index modulating area is formed in the opticalwaveguide region of an optical waveguide. Thus, even when thediffraction efficiency distribution of phase grating deviates from itsdesirable distribution, a diffraction grating device having a desirablecharacteristic is made.

[0067] From the invention thus described, it will be obvious that theinvention may be varied in many ways. Such variations are not to beregarded as a departure from the spirit and scope of the invention, andall such modifications as would be obvious to one skilled in the art areintended for inclusion within the scope of the following claims.

What is claimed is:
 1. A method of making a diffraction grating device,in which an optical waveguide is irradiated, by way of a phase grating,with refractive index modulation inducing light capable of inducing arefractive index modulation in an optical waveguide region of saidoptical waveguide so as to form a diffraction grating in said opticalwaveguide region, said method comprising: a diffraction efficiencydistribution measuring step of measuring a diffraction efficiencydistribution of said phase grating; and a refractive index modulatingstep of irradiating said optical waveguide with said refractive indexmodulation inducing light by way of said phase grating with an amount ofirradiation of said refractive index modulation inducing light at eachposition on said phase grating being adjusted according to saiddiffraction efficiency distribution measured in said diffractionefficiency distribution measuring step, so as to modulate a refractiveindex of said optical waveguide region.
 2. A method of making adiffraction grating device according to claim 1, wherein saiddiffraction efficiency distribution measuring step is carried out priorto said refractive index modulating step.
 3. A method of making adiffraction grating device according to claim 1, wherein saiddiffraction efficiency distribution measuring step is carried outsimultaneously with said refractive index modulating step; and whereinsaid amount of irradiation of refractive index modulation inducing lightat each position on said phase grating is feedback-controlled accordingto said diffraction efficiency distribution of phase grating measured insaid diffraction efficiency distribution measuring step.
 4. A method ofmaking a diffraction grating device according to claim 1, wherein saidrefractive index modulation inducing light is made incident on saidphase grating while being scanned in a longitudinal direction of saidoptical waveguide in said refractive index modulating step, and theintensity of said refractive index modulation inducing light irradiatingeach position on said phase grating is adjusted upon said scanning.
 5. Amethod of making a diffraction grating device according to claim 1,wherein said refractive index modulation inducing light is made incidenton said phase grating while being scanned in a longitudinal direction ofsaid optical waveguide in said refractive index modulating step, and thescanning speed of said refractive index modulation inducing lightirradiating each position on said phase grating is adjusted upon saidscanning.
 6. A diffraction grating device made by the method of making adiffraction grating device according to claim
 1. 7. An apparatus formaking a diffraction grating device, in which an optical waveguide isirradiated, by way of a phase grating, with refractive index modulationinducing light capable of inducing a refractive index modulation in anoptical waveguide region of said optical waveguide so as to form adiffraction grating in said optical waveguide region, said apparatuscomprising: diffraction efficiency distribution measuring means formeasuring a diffraction efficiency distribution of said phase grating;and refractive index modulating means for irradiating said opticalwaveguide with said refractive index modulation inducing light by way ofthe phase grating with an amount of irradiation of said refractive indexmodulation inducing light at each position on said phase grating beingadjusted according to said diffraction efficiency distribution measuredby said diffraction efficiency distribution measuring means, so as tomodulate a refractive index of said optical waveguide region.
 8. Anapparatus for making a diffraction grating device according to claim 7,wherein said diffraction efficiency distribution measuring meansmeasures said diffraction efficiency distribution of said phase gratingbefore said refractive index modulating means irradiates said phasegrating with said refractive index modulation inducing light.
 9. Anapparatus for making a diffraction grating device according to claim 7,wherein said diffraction efficiency distribution measuring meansmeasures said diffraction efficiency distribution of said phase gratingat the same time when said refractive index modulating means irradiatessaid phase grating with said refractive index modulation inducing light;and wherein said refractive index modulating means feedback-controlssaid amount of irradiation of refractive index modulation inducing lightat each position on said phase grating according to said diffractionefficiency distribution of phase grating measured by said diffractionefficiency distribution measuring means.
 10. An apparatus for making adiffraction grating device according to claim 7, wherein said refractiveindex modulating means comprises: irradiating means for making saidrefractive index modulation inducing light incident on said phasegrating while scanning said refractive index modulation inducing lightin a longitudinal direction of said optical waveguide; and irradiationintensity adjusting means for adjusting the intensity of said refractiveindex modulation inducing light irradiating each position on said phasegrating when said refractive index modulation inducing light is scannedby said irradiating means.
 11. An apparatus for making a diffractiongrating device according to claim 7, wherein said refractive indexmodulating means comprises: irradiating means for making said refractiveindex modulation inducing light incident on said phase grating whilescanning said refractive index modulation inducing light in alongitudinal direction of said optical waveguide; and scanning speedadjusting means for adjusting the scanning speed of said refractiveindex modulation inducing light irradiating each position on said phasegrating when said refractive index modulation inducing light is scannedby said irradiating means.
 12. An apparatus for making a diffractiongrating device, in which a diffraction grating is made in an opticalwaveguide region of an optical waveguide, said apparatus comprising: alight source for emitting refractive index modulation inducing lightcapable of inducing a refractive index modulation in said opticalwaveguide region; a phase grating for diffracting said refractive indexmodulation inducing light emitted from said light source; a mirror forreflecting said refractive index modulation inducing light emitted fromsaid light source so as to make said refractive index modulationinducing light incident on said phase grating; a moving unit for movingsaid mirror along a longitudinal direction of said optical waveguide;and a speed control unit for controlling, according to a diffractionefficiency distribution of said phase grating, the moving speed of saidmirror moved by said moving unit.
 13. An apparatus for making adiffraction grating device, in which a diffraction grating is made in anoptical waveguide region of an optical waveguide, said apparatuscomprising: a light source for emitting refractive index modulationinducing light capable of inducing a refractive index modulation in saidoptical waveguide region; a phase grating for diffracting saidrefractive index modulation inducing light emitted from said lightsource; a mirror for reflecting said refractive index modulationinducing light emitted from said light source so as to make saidrefractive index modulation inducing light incident on said phasegrating; a moving unit for moving said mirror along a longitudinaldirection of said optical waveguide; and an irradiation intensitycontrol unit for controlling the irradiation intensity of saidrefractive index modulation inducing light emitted from said lightsource.
 14. An apparatus for making a diffraction grating deviceaccording to claim 12 or 13, further comprising a light-receiving deviceprovided so as to sandwich said phase grating between saidlight-receiving device and said mirror.